The rolling of external profiles refers to the noncutting production of external profiles by cold forming, where the profile is milled into the surface of the corresponding blank.
The shaping process is based on the generation of compressive strains by one or more tools that reproduce shapes on the workpiece.
The advantages over a machine-cutting production reside most notably in the greater fatigue strength that is obtained due to the uninterrupted grain-flow pattern and, at the same time, in an achievable surface hardening.
In contrast to cutting processes, the grain boundaries are not interrupted; moreover, the notch sensitivity is reduced, as is the friction due to the smoother surface.
Thread rolling is mainly used in the industrial production of screws and threaded spindles or bolts. An external profile can be milled using cylindrical thread-rolling dies in radial or through-feed rolling processes.
Cold-forming processes are used in practice to produce large lot sizes in the manufacturing of standardized nuts and screws.
In thread rolling processes using flat thread-rolling dies, the set of dies is provided with the thread mating profile having the lead angle of the thread, one die being fixed and the other movable. The workpiece is then rolled between the flat dies.
Thread rolling using cylindrical thread-rolling dies can be carried out in radial or through-feed rolling processes. In radial rolling processes, the workpiece is held by a straightedge and, in through-feed rolling processes, it is clamped between points. In radial rolling processes, the rolls have a mating profile which has the same lead angle as the rolled thread. The axes of rotation of the workpiece and of the tools must extend in parallel to one another. Each roll pair can only be used for one specific thread.
In through-feed rolling processes, the profiling tools have mutually adjacent, pitchless thread profiles. They are tilted by the requisite lead angle about the horizontal longitudinal axis. They can also be used to a limited extent for smaller workpiece diameters.
The German Utility Model Patent 77 38 892 U1 describes a device for producing threads on workpieces, in particular pipes. The device has a frame, whose mutually parallel longitudinal parts are designed in the form of a slide rail, and has a sliding carriage that is slideable on these longitudinal parts and that has a motor attached thereto. In addition, the device has a clamping device for clamping the workpiece coaxially to the axis of the rolling head. In this context, a plurality of elongated ribs are provided, which, on one edge, each have a working profile that is used for machining a blank of a fastening device, a thread being produced on the blank by rolling. The ribs are configured side-by-side and are fixed to one another, the working profile for forming a tool being configured on the same side.
In addition, the International Patent Application WO 01/68288 A1 also already describes a thread rolling device which has two profiling tools adapted for radial infeed.
The German Patent Application DE 32 45 266 A1 discusses a thread rolling attachment adapted for radial infeed, including two die elements, which are each equipped with means for mounting a profiling tool at one end, as well as with a roll that is fastened to the other end. The die elements are swivel-mounted opposite one another on the housing.
In addition, a method, referred to as thread pressing, is also already known for producing round threads in relatively thin sheet metal. In this context, the thread is pressed by two profiled rolls into the workpiece.
The aforementioned devices have in common that they are installations suited for industrial use. Therefore, a mobile on-site use is not possible, particularly when working with stationary devices.
Moreover, without an electrical power supply, the use of such devices is ruled out.
To the extent that it is necessary to introduce threads on-site into pipes or rods, for example, for installation or assembly purposes, thread cutting is carried out in practice exclusively using thread-cutting dies or die stocks.
Thread-cutting dies or die stocks are generally used for manual cutting processes and for threads having low accuracy requirements. In the case of die stocks, no backward rotation is required. The thread-cutting die is used exclusively for cutting external threads and, on the inside, has three or more cutting edges. Between the cutting edges, hollow spaces are incorporated for curling and carrying away the chips that form. The cutting edges are serrated and, geometrically, represent the internal thread.
To cut an external thread, the workpiece must already have the nominal diameter of the desired thread. The workpiece is torsionally fixed on one side by the side, the thread-cutting die is applied and rotated until the desired thread length is achieved.
In addition, hexagonal thread-cutting dies are also known from the related art, which can be moved to inaccessible locations using a box wrench or open-end wrench.
The inherent disadvantage of such mobile thread-cutting devices is, on the one hand, that the thread can only be introduced beginning at one free end.
Thus, it is not possible to introduce a thread into a workpiece that is supported at both ends. On the other hand, chip-forming machining during thread cutting leads to a reduction in material thickness and thus in strength.
The Patent Application DE 699 13 633 T describes a form of a pipe cutter that is designed as a portable handheld device. The pipe cutter is equipped with a cutter roll, as well as with two mutually opposing pressure rolls that form a locking element. A threaded rod, which is mounted in a threaded sleeve, permits a feed movement of the cutter roll relative to the pressure rolls via a handle. Therefore, these are cutting machining processes.